Michael Fallon: ‘We cannot predict the situations that the UK and its armed forces may face in future.’
Photograph: Andy Rain/EPA

Ministers have abandoned plans to introduce a war powers act that would enshrine into law a commitment to seek parliamentary approval before deploying British troops in combat.

Michael Fallon, the defence secretary, told MPs: “I should … emphasise that the prime minister and I have to take decisions about the deployment of ships and planes and troops.” They did not want to be “artificially constrained in action to keep this country safe”, he said.

Fallon, who first announced the decision in a written Commons answer, told MPs later that ministers would “keep parliament informed and we will of course seek its approval before deploying British forces in combat roles into a conflict situation”.

Asked whether the timing of the written statement was linked to the foreign secretary Philip Hammond’s visit to Libya, amid speculation about UK involvement in a possible international military assistance force, the prime minister’s official spokeswoman said: “It would be wrong to make any connection.”

Calls for a war powers act grew after the military interventions in Iraq, Afghanistan, and Libya. But ministers have decided that such a statute would restrict their freedom of action, subject them to possible legal action, and get them embroiled in arguments about the definition of training and combat missions.

“We cannot predict the situations that the UK and its armed forces may face in future,” Fallon said in his written statement. “If we were to attempt to clarify more precisely circumstances in which we would consult parliament before taking military action, we would constrain the operational flexibility of the armed forces and prejudice the capability, effectiveness or security of those forces, or be accused of acting in bad faith if unexpected developments were to require us to act differently.”

The cabinet manual states: “In 2011 the government acknowledged that a convention had developed in parliament that before troops were committed, the House of Commons should have an opportunity to debate the matter, and said that it proposed to observe that convention except where there was an emergency and such action would not be appropriate.”

Fallon said the prime minister had made such a commitment in relation to Libya on 16 March this year. The convention did not apply to British military personnel embedded in the armed forces of other nations, Fallon added.

The prime minister has the final say on deploying British troops in conflicts, using royal prerogative powers. In 2006, when he was opposition leader, David Cameron said trust in politics could only be restored if MPs had the final say on committing troops to war.